Multiple description (MD) coding is a source coding technique in which multiple bit streams are used to describe a given source signal. Each of these bit streams represents a different description of the signal, and the bit streams can be decoded separately or in any combination. Each bit stream may be viewed as corresponding to a different transmission channel subject to different loss probabilities. The goal of MD coding is generally to provide a signal reconstruction quality that improves as the number of received descriptions increases, without introducing excessive redundancy between the descriptions.
By way of example, two-description MD coding is characterized by two descriptions having rates R1 and R2 and corresponding single-description reconstruction distortions D1 and D2, respectively. The single-description distortions D1 and D2 are also referred to as side distortions. The distortion resulting from reconstruction of the original signal from both of the descriptions is designated D0 and referred to as the central distortion. Similarly, the corresponding single-description and two-description decoders are called side and central decoders, respectively. A balanced two-description MD coding technique refers to a technique in which the rates R1 and R2 are equal and the expected values of the side distortions D1 and D2 are equal.
A well-known MD coding approach known as MD scalar quantization (MDSQ) is described in V. A. Vaishampayan, “Design of multiple description scalar quantizers,” IEEE Transactions on Information Theory, Vol. 39, No. 3, pp. 821–834, May 1993, which is incorporated by reference herein. In an example of two-description MDSQ, a given signal sample is quantized using two different scalar quantizers, and each quantizer output is transmitted on a corresponding one of two different channels. If either channel is received by itself, the original signal sample value is known within a given quantization cell of that channel. If both channels are received, the original value is known within the intersection of its quantization cell in one channel and its quantization cell in the other. In this manner, an MDSQ system provides coarse information to side decoders and finer information to a central decoder.
Although these and other MD coding techniques are well known in the art, a need nonetheless exists for improvements in the implementation of MD coding in practical applications, particularly in wireless communication system applications such as frequency hopping wireless systems.